Conventional surface protective layers and interlayer insulating layers for semiconductor devices include a polyimide resin, which can have excellent heat resistance, electrical characteristics, mechanical characteristics, and the like. The polyimide resin has recently been used as a photosensitive polyimide precursor composition which can be coated easily. The photosensitive polyimide precursor composition is coated on a semiconductor device, patterned by ultraviolet (UV) rays, developed, and heat imidized to provide a surface protective layer, an interlayer insulating layer, and the like. Accordingly, it is possible to significantly shorten the processing time compared with that of a conventional non-photosensitive polyimide precursor composition.
The photosensitive polyimide precursor composition can be applied as a positive type in which an exposed part is dissolved by development, or a negative type in which the exposed part is cured and maintained. Positive type photosensitive compositions can be developed by a non-toxic alkali aqueous solution. The positive photosensitive polyimide precursor composition can include a polyimide precursor of polyamic acid, a photosensitive material of diazonaphthoquinone, and the like. However, it can be difficult to obtain the desired pattern using the positive photosensitive polyimide precursor composition because the carbonic acid of the polyamic acid can be too highly soluble in an alkali.
Japanese Patent Laid-Open Publication No. Pyeung 11-202488 is directed to a photosensitive polyimide precursor composition including a polyimide resin obtained from a dehydration reaction of an aromatic acid dianhydride having a phenolic hydroxy group with aromatic diamine and diazonaphthoquinone.
The diazonaphthoquinone reacts with a phenolic hydroxy group in the polyimide resin and can suppress the polyimide resin from being dissolved in an alkali aqueous solution. The diazonaphthoquinone can be decomposed by light and can produce a ketene group. The diazonaphthoquinone also can react with water and produce a carboxyl group. Accordingly, the photosensitive polyimide resin film may have a large dissolubility difference for an alkali aqueous solution between an exposed part and an unexposed part. As a result, when the photosensitive polyimide resin film is developed using an alkali aqueous solution, the exposed part may be removed by the alkali aqueous solution, forming a positive photosensitive polyimide resin composition pattern.
Generally, in order to form a fine pattern in a short time when an exposed photosensitive polyimide resin thin film is developed, a tetramethylammonium hydroxide (TMAH) aqueous solution is used. The alkali concentration of a TMAH aqueous solution, however, can be hard to control and the TMAH aqueous solution is not necessarily safe for a human body.
In general, it is well known to esterify a compound having a phenolic dydroxy group with quinone diazide sulfonic acid and use the esterified compound as a photoresist in a resist composition for a fine semiconductor process. In other words, when a composition including a novolac resin and a compound having a quinone diazide group is coated on a substrate and radiated by a light with a wavelength ranging from about 300 to about 500 nm, the quinone diazide group is decomposed and produces a carboxyl group, which makes the composition soluble in alkali. Accordingly, the composition may be used as a positive resist. This positive resist can have excellent resolution compared with a negative resist and thus may be used to fabricate various kinds of integrated circuits for a semiconductor.
Recently, integrated circuits are becoming more highly integrated and thus there is a need to micronize the same and provide sub-micron patterns. In order to form the sub-micron pattern, a lithography process plays a very important role in fabricating an integrated circuit, and the positive resist is required to have improved resolution.
There are limitations to prior techniques for preparing a resist material including a quinone diazide compound and a novolac resin by combining each component. For example, U.S. Pat. No. 5,153,096 discloses a method of esterifying a triphenyl methane-based compound having at least two phenolic hydroxy groups with quinone diazide sulfonic acid to use it as a photoresist. However, the photoresist is not still satisfactory to be used for an extreme microprocess to fabricate a very large scale integrated direct circuit, what is called, for sub-micron lithography.